In accordance with the advance in the display industry, a low driving voltage, realization of high resolution, reduction in volume of a monitor, and flatness of a monitor have been provided, and thus, a demand for such the, liquid crystal display is significantly growing. In these liquid crystal display technologies, it is one of the essential techniques to align liquid crystals in a desired direction.
Conventionally, as a common method for aligning the liquid crystal, there has been used a contact-type rubbing process comprising applying a polymer film formed of a polymer such as polyimide on a substrate such as glass, and rubbing a surface of the resulting substrate using fibers such as nylon and polyester in a predetermined direction. However, in the contact-type rubbing process, fine dust may be generated or electrostatic discharge (ESD) may occur when the fibroid materials are rubbed with the polymer film, and severe problems may occur during the production of liquid crystal panels due to the troubles of the process.
Therefore, many studies have been recently made to produce an aligning layer using a novel contactless-type process in order to avoid the above problems of the contact-type rubbing process.
Examples of the contactless-type process of producing the aligning layer include an optical alignment process, an energy beam alignment process, a vapor deposition alignment process, and an etching process using lithography. Among these processes, the most realizable process is an optical alignment process, in which a linearly polarized light is radiated on a photosensitive polymer thin layer, to cause an anisotropic chemical reaction, and as a result to induce liquid crystal aligning.
The optical alignment process can be classified into optical isomerization, optical polymerization, and optical resolution processes, according to its reaction mechanism. Among them, the optical resolution has greatly attracted attention, which uses a polyimide thin layer, previously widely commercialized as an aligning layer. The polyimide for the optical resolution is a polymer in the linear form. The optical resolution inevitably leads to generation of the decomposed by-products in the small units by selectively photo-decomposing the polymer backbone consistent with the linearly polarized light and inducing the liquid crystal aligning, thereby photo-decomposing the polyimide. Such the decomposed by-product can cause very serious problem in the view of alignment stability and long-term reliability, particularly image sticking, practically upon the preparation of a liquid crystal display. The problem caused in the view of alignment stability, long-term reliability, and image sticking is arising as the largest problem which blocks the commercialization of the optical alignment process.
Therefore, there exists a need of a liquid crystal aligning layer, obtained by removing the decomposed by-products of the polyimide generated by the optical resolution, and thus promoting the alignment stability, and improving long-term reliability and image sticking.